SAPHE: simple accelerometer based wireless pairing with heuristic trees

Accelerometers provide a good source of entropy for bootstrapping a secure communication channel in autonomous and spontaneous interactions between mobile devices that share a common context but were not previously associated. We propose two simple and efficient key exchange protocols based on accelerometer data that use only simple hash functions combined with heuristic search trees. Using heuristics such as the Euclidean distance proves to be beneficial as it allows a more effective recovery of the shared key. While the first protocol seems to give just some performance improvements, the second, which we call hashed heuristic tree, is more secure than previous proposals since it increases the difference in protocol execution between benign and malicious parties. Nevertheless, the hashed heuristic tree is an entirely new approach which has the advantage of allowing different heuristics in the search, leaving plenty of room for future variants and optimizations.